Hydraulic bucket tappet

ABSTRACT

A hydraulic tappet for internal combustion engines with overhead camshaft has hollow cylindrical housing that is sealed at one end by a tappet floor that is mechanically linked to a cam of a camshaft. Longitudinally borne in the housing is a hydraulic play compensation unit, the pressure chamber of which, for exchanging fluid, can be connected to a fluid reservoir that is sealed to the outside. For compensating volume from the fluid reservoir, a largely circular compensation element that limits the fluid reservoir is provided and that is provided with at least one undulation and/or fold. The compensation element is arranged such that the center region is freely movable and the undulation and/or fold opens or closes depending on the required volume compensation.

[0001] The invention relates to a hydraulic tappet for an internalcombustion engine with an overhead camshaft in accordance with thepreamble to claim 1.

[0002] A generic hydraulic tappet is known from DE 41 36 746 A1.

[0003] The generic document illustrates a hydraulic tappet for internalcombustion engines with a housing in which is arranged a playcompensation element joined concentrically to at least one fluidreservoir. The fluid reservoir is completely sealed to the outside andthe hydraulic tappet consequently works with an internal oil supply.

[0004] Automatic hydraulically adjusting play compensation elements, inparticular those in tappets of internal combustion engines, areconstructed such that during the lift phase of the cam, due to a pistondisplacement hydraulic fluid is pressed out of a pressure chamber in theplay compensation element through a choke channel into a reservoir. Aspring restores the piston in the base circle phase of the cam, wherebya non-return valve in a channel opens and hydraulic fluid flows backfrom the reservoir into the pressure chamber. In the lift phase thepiston displacement generally reduces the size of the reservoir. Volumecompensation elements are necessary in order, nevertheless, to be ableto receive the hydraulic fluid exiting the pressure chamber.

[0005] Known from DE 41 25 568 A1 is the arrangement of spring-loadedelements in the fluid reservoir.

[0006] Elastomer membranes that are employed for volume compensation areknown from DE 39 10 666 C2. The membranes are curved and are arrangedbetween an exterior surface of the play compensation element and aninterior surface of the housing. However, due to contact with oil, themembranes have substantial disadvantages in terms of permeation andchanges in hardness and associated poor cold flexibility. It is alsodisadvantageous that leaks can occur, since the membranes are alsosubject to stretching due to the annular embodiment and the limitedspace for volume compensation. In addition, the membranes also seal themovable components, and failure due to tears occurs over the servicelife under vehicle conditions.

[0007] The function of the hydraulic tappet is negatively affected bythe support of the membranes on the play compensation element. First ofall, this can lead to the hydraulic tappet becoming jammed, and,secondly, it can mean that tolerance compensation is not assured.

[0008] Another hydraulic tappet with an integrated reservoir is knownfrom DE 41 30 529 A1. One membrane element constituting two layers isemployed. The membrane element is arranged analogous to the membraneelement described in DE 39 10 666 C2, radially on the interior surfaceof the housing and on the exterior surface of the play compensationelement. The disadvantages cited with respect to DE 39 10 666 C2 interms of being leak-proof, the stress of stretching, and the negativeeffect of the hydraulic tappet apply similarly.

[0009] The generic document, DE 41 36 746 A1, provides that the totalvolume from the pressure chamber and reservoir remains constant withoutfluid forces having to act on the volume compensation elements. When thepiston moves, the volume of the pressure chamber decreases/increases bythe same amount as the volume of the reservoir increases/decreases.Thus, actual volume compensation is not necessary. In one illustratedembodiment, two partial reservoirs are provided that are arrangedaxially on either side of the pressure chamber. Flexible membranes thatseal these are provided at each axially exteriorly situated end of thepartial reservoirs. Also provided in this embodiment is that the volumeof the pressure chamber decreases/increases by the same amount as thevolume of the two partial reservoirs increases/decreases. The membranesmake it possible for the play compensation element to be employed evenwhen it is expected that there will be thermally-caused changes in thedensity of the hydraulic fluid in the pressure chamber and reservoir(column 5, lines 4-8).

[0010] The membranes described in DE 41 36 746 A1 are attached analogousto the membranes known from DE 39 10 666 C2 and DE 41 30 529 A1, and thesame disadvantages apply. Although the stress on the membranes is lowersince the membranes are not employed for compensating volume, themembranes still also seal the moving parts and are thereforecorrespondingly stressed. The thermally-caused change in density in thehydraulic fluid is received by the membranes in accordance with DE 41 36746 A1 by stretching. In one embodiment that is not illustrated, it isprovided that one of the membranes is just placed loose on the end faceof a compensation rod so that when there is thermally induced fluidexpansion, the compensation rod lifts the membrane. This reducesstretching of the membrane. However, a corresponding stress or evendamage to the membrane results due to impacts or the like result,depending on the movement of the compensation rod upon which themembrane is situated.

[0011] None of the known hydraulic tappets with a fluid reservoir thatis sealed to the outside has proved itself in practice, since leakscould not be reliably prevented over the service life under vehicleconditions. In general the membranes are stressed the most at theconnecting points and consequently leak there.

[0012] An object of the present invention is to provide a hydraulictappet for internal combustion engines with a fluid reservoir that issealed to the outside, which tappet overcomes the aforesaiddisadvantages of the prior art, in particular, is sealed for theprovided service life, provides optimal functioning, and is simple andcost-effective to produce.

[0013] This object is achieved inventively by the characterizing portionof claim 1.

[0014] The undulation and/or fold in the inventive compensation elementadvantageously receives and then releases the corresponding fluid volumewith almost no pressure. The center region is freely movable and is notjoined to the play compensation element or to a piston, as in thehydraulic tappet known from prior art. Thus the compensation elementmerely receives the volume compensation role and does not also seal themoving components. These two functions are thus separated. Thus, provenmovement seals such as for instance O-rings, rod seals, O-ring supportedsealing rings, V-rings, or the like can be employed for sealing themoving components.

[0015] As was determined in trials, the inventive hydraulic tappet isparticularly suitable for employment in practice. Leaks at theconnection points to the compensation element do not occur, since nomovement has to be sealed thereby. In addition, since volumecompensation occurs when the undulation and/or fold opens or closes, thecompensation element is not or is largely not stressed by stretching,which means that the service life clearly increases. Since the centerregion of the compensation element is freely movable and consequently isnot in contact with the play compensation unit or a piston, thefunctioning of the hydraulic tappet is not negatively affected. Thehydraulic tappet cannot be jammed, therefore. Tolerance compensation isassured at all times.

[0016] Advantageously, the compensation element has only onecircumferential sealing site which simultaneously represents theattachment.

[0017] It is advantageous when the compensation element is embodied as abellows.

[0018] In trials, it was demonstrated that an embodiment as bellows isparticularly suited for opening or closing the undulation and/or foldwith almost no pressure. In one preferred embodiment it can be providedthat the bellows is made of rubber or synthetic rubber.

[0019] In accordance with the invention, it can furthermore be providedthat the housing is sealed in the direction of the camshaft by a tappetfloor and a bushing, whereby the tappet floor and the bushing aredisplaceably arranged in the housing and whereby the bellows is clampedbetween the bushing and the tappet floor. Advantageously, the bellowscan be dimensioned like an O-ring in this region.

[0020] With respect to attaching the bellows in the most simple and mostlasting possible manner, such an arrangement has proved particularlysuitable. Thus, the bellows merely accomplishes the volume compensationfunction and no movement seal is required. Due to the O-ring-typecross-section of the bellows on the exterior circumference, it can beeasily pressed in or compressed between the bushing and the tappetfloor. A lasting and sealed connection is thus provided.

[0021] In one alternative embodiment of the invention, it can beprovided that the bellows is vulcanized at the bushing and/or at thetappet floor.

[0022] In trials it was demonstrated that vulcanizing the bellows at thetappet floor or bushing can likewise provide a secure attachment thatseals lastingly. Naturally other joining or attaching methods can beemployed alternative to vulcanization, such as e.g. adhesives,soldering, or welding.

[0023] Advantageous embodiments and further developments of theinvention result from the additional subordinate claims and from thefollowing exemplary embodiment, the principles of which are illustratedusing the drawing.

[0024] The only figure in the drawing illustrates an inventive hydraulictappet with a play compensation element.

[0025] As can be seen from the figure, the hydraulic tappet 1 has ahollow cylindrical housing 2 that is sealed at one end by a tappet floor5 that is mechanically linked to a cam 3 of a camshaft 4. The hydraulictappet 1 is provided for a internal combustion engine (not shown) withthe overhead camshaft 4. Longitudinally borne in the housing 2 is ahydraulic play compensation unit 6, the pressure chamber 7 of which, forexchanging fluid, can be connected to a fluid reservoir 8 that is sealedto the outside. The principle upon which the play compensation unit 6functions is well-known from the prior art (see for instance DE 39 10666 C2), for which reason it will not be described in greater detail inthe following.

[0026] As can be seen from the figure, the hydraulic tappet 1, forcompensating volume from the fluid reservoir 8, has a largely circularcompensation element 9 that limits the fluid reservoir 8. Thecompensation element 9 is arranged such that it is not situated in thepower force between the cam 3 and a valve lifter 21. The compensationelement 9 is consequently situated outside of the power force.

[0027] The compensation element 9 in the exemplary embodiment isdesigned as a bellows 9 and has an undulation 10 which opens or closesdepending on the required volume compensation. The opening and closingof the undulation 10 occurs with almost no pressure. In one alternativeembodiment it can also be provided that the bellows 9 has a plurality ofundulations and/or folds 10.

[0028] As can also be seen from the figure, the center region 11 of thebellows 9 is freely movable. In the exemplary embodiment, the centerregion 11 of the bellows 9 extends almost to the exterior circumferenceof the bellows 9.

[0029] The housing 2 has a housing floor 2 a embodied integrally withthe housing 2 at the side facing away from the tappet floor 5. The playcompensation unit 6 stands on this housing floor 2 a. The housing issealed in the direction of the camshaft 4 by the tappet floor 5 and abushing 12. The tappet floor 5 and the bushing 12 are displaceablyarranged in the housing 2. In order to assure the mobility of thehydraulic tappet 1, the bushing 12 is supported by a spring 13 that isarranged between the bushing 12 and the housing floor 2 a.

[0030] The fluid reservoir 8 is sealed by the housing 2, the bushing 12,and the bellows 9. The fluid is sealed in the housing 2 by a seal 14between the bushing 12 and the housing 2. The seal 14 is preferablyembodied as an O-ring. In the exemplary embodiment, the tappet floor 5thus has no contact with the fluid of the fluid reservoir 8 andtherefore also does not have to be sealed to the housing 2.

[0031] As can be seen from the figure, the bellows 9 is clamped betweenthe bushing 12 and the tappet floor 5. The bellows 9 has on its exteriorcircumference an O-ring-shaped form 9 a. This O-ring-shaped form 9 a canbe pressed in or compressed between the bushing 12 and the tappet floor5. The O-ring-shaped form 9 a, in which the bellows 9 terminates andwhich is illustrated in cross-section in the figure, is compressed bythe difference in the diameters of the bushing 12 and the tappet floor5, and thus seals. As can also be seen from the figure, the tappet floor5 has a free space 15 for receiving the opened fold 10. Thus therequired compensation volume is provided. The free space 15 can bemaintained with no pressure by an opening or pressure compensation unit(not shown) in the tappet floor 5.

[0032] If the hydraulic tappet 1 moves apart, a spring 17 presses apiston 16 of the play compensation unit 6 away from the floor of thehousing 18 of the play compensation element 6. Fluid is suctioned fromthe fluid reservoir 8 via a non-return valve 19 in a known manner.

[0033] As can be seen from the figure, the fluid reservoir 8 is situatedin the interior of the housing 2, in which the housing 18 of the playcompensation unit 6 is also situated.

[0034] When the hydraulic tappet 1 moves together, the bellows 9receives the volume that derives both from the displaced fluid from thepressure chamber 7 and from the decrease in the size of the fluidreservoir 8. The fold 10 folds into the free space 15 below the tappetfloor 5.

[0035] The power force between the cam 3 of the camshaft 4 and a valvelifter (not shown) is transferred as follows. The force is conducted viathe tappet floor 5 onto the bushing 12 and from there to the piston 16of the play compensation unit 6. From there the force travels via thetolerance-compensating non-compressible fluid (pressure chamber 7)enclosed in the play compensation element 6 to the housing 18 of theplay compensation unit 6, which stands on the housing floor 2 a of thehousing 2. The force is introduced to the housing floor 2 a directly bythe housing 18.

[0036] In the exemplary embodiment, the hydraulic tappet 1 is sealed bya retaining ring 20. Alternatively, any other known axial securingelement, such as for instance a locking ring, crimping of the container,or the like can be employed.

[0037] The spring 13 between the housing 2 and the bushing 12, whichcompensates the increased friction in the system and is responsible forrapid and precise adjusting of the hydraulic tappet 1, can be omitted ifthe spring 17 between the piston 15 and the housing 18 of the playcompensation unit 6 assumes this function.

[0038] Preferably the bellows 9 is produced from rubber or syntheticrubber. Alternatively, of course, the bellows 9 can also be producedfrom any other desired material that enables the fold 10 to open andclose to the greatest extent possible with no pressure.

[0039] Legend

[0040]1 Hydraulic tappet

[0041]2 Housing

[0042]2 a Housing floor

[0043]3 Cam

[0044]4 Camshaft

[0045]5 Tappet floor

[0046]6 Play compensation unit

[0047]7 Pressure chamber

[0048]8 Fluid reservoir

[0049]9 Compensation element

[0050]9 a Form

[0051]10 Undulation/fold

[0052]11 Center region

[0053]12 Bushing

[0054]13 Spring

[0055]14 Seal

[0056]15 Free space

[0057]16 Piston

[0058]17 Spring (play compensation unit)

[0059]18 Housing (play compensation unit)

[0060]19 Non-return valve

[0061]20 Retaining ring

[0062]21 Valve lifter

1. Hydraulic tappet for internal combustion engines with an overheadcamshaft, comprising a hollow cylindrical housing that is sealed at oneend by a tappet floor that is mechanically linked to a cam of thecamshaft, a hydraulic play compensation unit in said housing, saidhydraulic play compensation unit having a pressure chamber of which, forexchanging fluid, can be connected to a fluid reservoir that is sealedto the outside wherein for compensating the volume from said fluidreservoir, a compensation element that limits the fluid reservoir andprovided with at least one undulation and/or folds is provided, wherebysaid compensation element being arranged such that the center regionthereof is freely movable and said undulation and/or fold opens orcloses depending on the required volume compensation.
 2. Hydraulictappet in accordance with claim 1, wherein said compensation element isarranged outside of the power force between said cam and a valve lifter.3. Hydraulic tappet in accordance with claim 1 or 2, wherein saidcompensation element is embodied such that said undulation and/or foldopens and closes with almost no pressure.
 4. Hydraulic tappet inaccordance with claim 1 or 2 wherein said compensation element is abellows.
 5. Hydraulic tappet in accordance with claim 1 or 2, whereinsaid housing has a housing floor integral with said housing at the sidefacing away from said tappet floor.
 6. Hydraulic tappet in accordancewith claim 5, wherein said compensation element stands on said housingfloor.
 7. Hydraulic tappet in accordance with claim 1 or 2, wherein saidhousing is sealed in the direction of said camshaft by said tappet floorand a bushing.
 8. Hydraulic tappet in accordance with claim 7, whereinsaid tappet floor and said bushing are displaceably arranged in saidhousing.
 9. Hydraulic tappet in accordance with claim 7, comprising aspring is arranged between said bushing and said housing floor. 10.Hydraulic tappet in accordance with claim 7, wherein a seal is arrangedbetween said bushing and said housing.
 11. Hydraulic tappet inaccordance with claim 7, wherein said bellows is clamped between saidbushing and said tappet floor.
 12. Hydraulic tappet in accordance withclaim 11, wherein said bellows has on its exterior circumference anO-ring-shaped form that can be pressed in or compressed between saidbushing and said tappet floor.
 13. Hydraulic tappet in accordance withclaim 7, wherein said bellows is vulcanized at said bushing and/or atsaid tappet floor.
 14. Hydraulic tappet in accordance with claim 1 or 2,wherein said tappet floor has a free space for receiving said openedundulation and/or fold.
 15. Hydraulic tappet in accordance with claim14, wherein said free space is maintained with no pressure by an openingin said tappet floor.
 16. Hydraulic tappet in accordance with claim 10,wherein said seal is an o-ring.